This invention relates to the use of a series of pyrazolo[4,3-d]pyrimidin-7-ones for the treatment of impotence.
Impotence can be defined literally as a lack of power, in the male, to copulate and may involve an inability to achieve penile erection or ejaculation, or both. More specifically, erectile impotence or dysfunction may be defined as an inability to obtain or sustain an erection adequate for intercourse. Its prevalence is claimed to be between 2 and 7% of the human male population, increasing with age, up to 50 years, and between 18 and 75% between 55 and 80 years of age. In the USA alone, for example, it has been estimated that there are up to 10 million impotent males, with the majority suffering from problems of organic rather than of psychogenic origin.
Reports of well-controlled clinical trials in man are few and the efficacy of orally administered drugs is low. Although many different drugs have been shown to induce penile erection, they are only effective after direct injection into the penis, e.g. intraurethrally or intracavernosally (i.c.), and are not approved for erectile dysfunction. Current medical treatment is based on the i.c injection of vasoactive substances and good results have been claimed with phenoxybenzamine, phentolamine, papaverine and prostaglandin E1, either alone or in combination; however, pain, priapism and fibrosis of the penis are associated with the i.c. administration of some of these agents. Potassium channel openers (KCO) and vasoactive intestinal polypeptide (VIP) have also been shown to be active i.c., but cost and stability issues could limit development of the latter. An alternative to the i.c. route is the use of glyceryl trinitrate (GTN) patches applied to the penis, which has been shown to be effective but produces side-effects in both patient and partner.
As a general alternative to pharmacological intervention, a variety of penile prostheses has been used to assist achievement of an erection. The short term success rate is good, but problems with infection and ischaemia, especially in diabetic men, make this type of treatment a final option rather than first-line therapy.
The compounds of the invention are potent inhibitors of cyclic guanosine 3xe2x80x2,5xe2x80x2-monophosphate phosphodiesterases (cGMP PDEs) in contrast to their inhibition of cyclic adenosine 3xe2x80x2,5xe2x80x2-monophosphate phosphodiesterases (cAMP PDEs). This selective enzyme inhibition leads to elevated cGMP levels which, in turn, provides the basis for the utilities already disclosed for the said compounds in EP-A-0463756 and EP-A-0526004, namely in the treatment of stable, unstable and variant (Prinzmetal) angina, hypertension, pulmonary hypertension, congestive heart failure, atherosclerosis, conditions of reduced blood vessel patency e.g. post-percutaneous transluminal coronary angioplasty (post-PTCA), peripheral vascular disease, stroke, bronchitis, allergic asthma, chronic asthma, allergic rhinitis, glaucoma, and diseases characterised by disorders of gut motility, e.g. irritable bowel syndrome (IBS).
Unexpectedly, it has now been found that these disclosed compounds are useful in the treatment of erectile dysfunction. Furthermore the compounds may be administered orally, thereby obviating the disadvantages associated with i.c. administration. Thus the present invention concerns the use of a compound of formula (I): 
wherein
R1 is H; C1-C3 alkyl; C1-C3 perfluoroalkyl; or C3-C5 cycloalkyl;
R2 is H; C1-C6 alkyl optionally substituted with C3-C6 cycloalkyl; C1-C3 perfluoroalkyl; or C3-C6 cycloalkyl;
R3 is C1-C6 alkyl optionally substituted with C3-C6 cycloalkyl; C1-C6 perfluoroalkyl; C3-C5 cycloalkyl; C3-C6 alkenyl; or C3-C6 alkynyl;
R4 is C1-C4 alkyl optionally substituted with OH, NR5R6, CN, CONR5R6 or CO2R7; C2-C4 alkenyl optionally substituted with CN, CONR5R6 or CO2R7; C2-C4 alkanoyl optionally substituted with NR5R6; (hydroxy)C2-C4 alkyl optionally substituted with NR5R6; (C2-C3 alkoxy)C1-C2 alkyl optionally substituted with OH or NR5R6; CONR5R6; CO2R7; halo; NR5R6; NHSO2NR5R6; NHSO2R8; SO2NR9R10; or phenyl, pyridyl, pyrimidinyl, imidazolyl, oxazolyl, thiazolyl, thienyl or triazolyl any of which is optionally substituted with methyl;
R5 and R6 are each independently H or C1-C4 alkyl, or together with the nitrogen atom to which they are attached form a pyrrolidinyl, piperidino, morpholino, 4-N(R11)-piperazinyl or imidazolyl group wherein said group is optionally substituted with methyl or OH;
R7 is H or C1-C4 alkyl;
R8 is C1-C3 alkyl optionally substituted with NR5R6;
R9 and R10 together with the nitrogen atom to which they are attached form a pyrrolidinyl, piperidino, morpholino or 4-N(R12)-piperazinyl group wherein said group is optionally substituted with C1-C4 alkyl, C1-C3 alkoxy, NR13R14 or CONR13R14;
R11 is H; C1-C3 alkyl optionally substituted with phenyl; (hydroxy)C2-C3 alkyl; or C1-C4 alkanoyl;
R12 is H; C1-C6 alkyl; (C1-C3 alkoxy)C2-C6 alkyl; (hydroxy)C2-C6 alkyl; (R13R14N)C2-C6 alkyl; (R13R14NOC)C1-C6 alkyl; CONR13R14; CSNR13R14; or C(NH)NR13R14; and
R13 and R14 are each independently H; C1-C4 alkyl; (C1-C3 alkoxy)C2-C4 alkyl; or (hydroxy)C2-C4 alkyl;
or a pharmaceutically acceptable salt thereof, or a pharmaceutical composition containing either entity, for the manufacture of a medicament for the curative or prophylactic treatment of erectile dysfunction in a male animal, including man.
In the above definition, unless otherwise indicated, alkyl groups having three or more carbon atoms, alkenyl and alkynyl groups having four or more carbon atoms, alkoxy groups having three carbon atoms and alkanoyl groups having four carbon atoms may be straight chain or branched chain. Halo means fluoro, chloro, bromo or iodo.
The compounds of formula (I) may contain one or more asymmetric centres and thus they can exist as enantiomers or diastereoisomers. Furthermore, certain compounds of formula (I) which contain alkenyl groups may exist as cis-isomers or trans-isomers. In each instance, the invention includes both mixtures and separate individual isomers.
The compounds of formula (I) may also exist in tautomeric forms and the invention includes both mixtures and separate individual tautomers.
The pharmaceutically acceptable salts of the compounds of formula (I) which contain a basic centre are, for example, non-toxic acid addition salts formed with inorganic acids such as hydrochloric, hydrobromic, sulphuric and phosphoric acid, with organo-carboxylic acids, or with organo-sulphonic acids. Compounds of formula (I) can also provide pharmaceutically acceptable metal salts, in particular non-toxic alkali metal salts, with bases. Examples include the sodium and potassium salts.
A preferred group of compounds of formula (I) is that wherein R1 is H, methyl or ethyl; R2 is C1-C3 alkyl; R3 is C2-C3 alkyl or allyl; R4 is C1-C2 alkyl optionally substituted with OH, NR5R6, CN, CONR5R6 or CO2R7; acetyl optionally substituted with NR5R6; hydroxyethyl optionally substituted with NR5R6; ethoxymethyl optionally substituted with OH or NR5R6; CHxe2x95x90CHCN; CHxe2x95x90CHCONR5R6; CHxe2x95x90CHCO2R7; CONR5R6; CO2H; Br; NR5R6; NHSO2NR5R6; NHSO2R8; SO2NR9R10; or pyridyl or imidazolyl either of which is optionally substituted with methyl; R5 and R6 are each independently H, methyl or ethyl, or together with the nitrogen atom to which they are attached form a piperidino, morpholino, 4-N(R11)-piperazinyl or imidazolyl group wherein said group is optionally substituted with methyl or OH; R7 is H or t-butyl; R8 is methyl or CH2CH2CH2NR5R6; R9 and R10 together with the nitrogen atom to which they are attached form a piperidino or 4-N(R12)-piperazinyl group wherein said group is optionally substituted with NR13R14 or CONR13R14; R11 is H, methyl, benzyl, 2-hydroxyethyl or acetyl; R12 is H, C1-C3 alkyl, (hydroxy)C2-C3 alkyl, CSNR13R14 or C(NH)NR13R14; and R13 and R14 are each independently H or methyl.
A more preferred group of compounds of formula (I) is that wherein R1 is methyl or ethyl; R2 is C1-C3 alkyl; R3 is ethyl, n-propyl or allyl; R4 is CH2NR5R6, COCH2NR5R6, CH(OH)CH2NR5R6, CH2OCH2CH3, CH2OCH2CH2OH, CH2OCH2CH2NR5R6, CHxe2x95x90CHCON(CH3)2, CHxe2x95x90CHCO2R7, CONR5R6, CO2H, Br, NHSO2NR5R6, NHSO2CH2CH2CH2NR5R6, SO2NR9R10, 2-pyridyl, 1-imidazolyl or 1-methyl-2-imidazolyl; R5 and R6 together with the nitrogen atom to which they are attached form a piperidino, 4-hydroxypiperidino, morpholino, 4-N(R11)-piperazinyl or 2-methyl-1-imidazolyl group; R7 is H or t-butyl; R9 and R10 together with the nitrogen atom to which they are attached form a 4-carbamoylpiperidino or 4-N(R12)-piperazinyl group; R11 is H, methyl, benzyl, 2-hydroxyethyl or acetyl; and R12 is H, C1-C3 alkyl, 2-hydroxyethyl or CSNH2.
A particularly preferred group of compounds of formula (I) is that wherein R1 is methyl or ethyl; R2 is n-propyl; R3 is ethyl, n-propyl or allyl; R4 is COCH2NR5R6, CONR5R6, SO2NR9R10 or 1-methyl-2-imidazolyl; R5 and R6 together with the nitrogen atom to which they are attached form a morpholino or 4-N(R11)-piperazinyl group; R9 and R10 together with the nitrogen atom to which they are attached form a 4-N(R12)-piperazinyl group; R11 is methyl or acetyl; and R12 is H, methyl, 2-propyl or 2-hydroxyethyl.
Especially preferred individual compounds of the invention include:
5-(2-ethoxy-5-morpholinoacetylphenyl)-1-methyl-3-n-propyl-1, 6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one;
5-(5-morpholinoacetyl-2-n-propoxyphenyl)-1-methyl-3-n-propyl-1, 6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one;
5-[2-ethoxy-5-(4-methyl-1-piperazinylsulphonyl)-phenyl]-1-methyl-3-n-propyl-1,6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one;
5-[2-allyloxy-5-(4-methyl-1-piperazinylsulphonyl)-phenyl]-1-methyl-3-n-propyl-1,6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one;
5-{2-ethoxy-5-[4-(2-propyl)-1-piperazinyl-sulphonyl]phenyl}-1-methyl-3-n-propyl-1,6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one;
5-{2-ethoxy-5-[4-(2-hydroxyethyl)-1-piperazinyl-sulphonyl]phenyl}-1-methyl-3-n-propyl-1,6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one;
5-{5-[4-(2-hydroxyethyl)-1-piperazinylsulphonyl]-2-n-propoxyphenyl}-1-methyl-3-n-propyl-1,6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one;
5-[2-ethoxy-5-(4-methyl-1-piperazinylcarbonyl)-phenyl]-1-methyl-3-n-propyl-1,6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one; and
5-[2-ethoxy-5-(1-methyl-2-imidazolyl)phenyl]-1-methyl-3-n-propyl-1,6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one.
The compounds of formula (I) and their pharmaceutically acceptable salts, processes for the preparation thereof, in vitro test methods for determining the cGMP PDE and cAMP PDE inhibitory activities thereof, pharmaceutical compositions thereof and routes of administration for human use, are described in EP-A-0463756 and EP-A-0526004.
A preliminary investigation was carried out with a view to isolating and characterising the cyclic nucleotide PDEs of human corpus cavernosum, relaxation of which leads to penile erection. Studies of substrate specificity, response to activators and inhibitor sensitivity, have demonstrated that human corpus cavernosum contains three distinct PDE enzymes.
Fresh frozen human penis was obtained from IIAM (Pennsylvania). Tissue was thawed at room temperature, the corpus cavernosum was dissected from the penis to yield approximately 2-4 g of tissue and the following isolation protocol was followed. Tissue was coarsely chopped in ice-cold isotonic buffer (35 ml) containing 250 mM sucrose, 1 mM EDTA, 0.5 mM PMSF and 20 mM HEPES, pH 7.2, and the mixture subjected to brief (1 min.) treatment with a Silversen mixer/emulsifier. Homogenates were prepared using homogeniser tubes with teflon pestles and soluble fraction was prepared by centrifugation at 100,000xc3x97g for 60 min. at 4xc2x0 C. 10 ml of high speed supernatant was applied to a Pharmacia Mono Q anion exchange column (1 ml bed volume) equilibrated with buffer containing 1 mM EDTA, 0.5 mM PMSF and 20 mM lhEPES, pH 7.2 (chromatography buffer). The column was then washed with 5 bed volumes of chromatography buffer, after which PDEs were eluted using a continuous gradient of 0-500 mM NaCl (total volume 35 ml) and 1 ml fractions collected.
Column fractions were assayed for PDE activity using 500 nM cGMP or 500 nM cAMP as substrate. cAMP PDE activity was also determined in the presence of 1 xcexcM unlabelled cGMP and the PDE activity of selected fractions was determined in the presence of 10 mM CaCl2 and 10 units/ml bovine brain calmodulin. Appropriate fractions were pooled and stored at 4xc2x0 C. during the course of the study.
Inhibition studies were performed using a substrate concentration of 500 nM throughout. All inhibitors were dissolved in DMSO and concentration-response curves were constructed over the range 3xc3x9710xe2x88x9210 to 1xc3x9710xe2x88x924 M in half log increments. IC50 values were calculated using the sigmoidal curve fitting algorithm of biostat.
Human corpus cavernosum soluble PDEs were separated into three distinct fractions of activity. The first, fraction I, (designated by order of elution) represents the major PDE present and is highly selective for cGMP as substrate. This fraction was found to be insensitive to stimulation by calcium/calmodulin and was classified as PDEV. Fraction II hydrolyses cGMP and cAMP, with the latter activity being stimulated in the presence of cGMP, and is classified as PDEII, whilst fraction III is cAMP selective and this activity is inhibited in the presence of cGMP, consistent with PDEIII activity.
In order to further characterise the PDE isoenzymes present in the tissue, studies were performed using a variety of inhibitors. Inhibitor studies with fractions I and II were performed using cGMP as substrate, whilst fraction III studies utilised cAMP. These studies confirmed that fraction I corresponds to PDEV, whilst fraction III was clearly identified as PDEIII; fraction II (PDEII) was relatively insensitive to all the inhibitors tested.
In summary, the above investigation identified three PDE isoenzymes in human corpus cavernosum tissue. The predominant PDE is the cGMP-specific PDEV, whilst cGMP-stimulated cAMP PDEII and cGMP-inhibited cAMP PDEIII are also present.
The compounds of the invention have been tested in vitro and found to be potent and selective inhibitors of the cGMP-specific PDEV. For example, one of the especially preferred compounds of the invention has an IC50=6.8 nM v. the PDEV enzyme, but demonstrates only weak inhibitory activity against the PDEII and PDEIII enzymes with IC50= greater than 100 xcexcM and 34 xcexcM respectively. Thus relaxation of the corpus cavernosum tissue and consequent penile erection is presumably mediated by elevation of cGMP levels in the said tissue, by virtue of the PDE inhibitory profile of the compounds of the invention.
Furthermore, none of the compounds of the invention tested in rat and dog, both intravenously (i.v.) and orally (p.o.) at up to 3 mg/Kg, has shown any overt sign of adverse acute toxicity. In mouse, no deaths occurred after doses of up to 100 mg/Kg i.v. Certain especially preferred compounds showed no toxic effects on chronic p.o. administration to rat at up to 10 mg/Kg and to dog at up to 20 mg/Kg.
In man, certain especially preferred compounds have been tested orally in both single dose and multiple dose volunteer studies. Moreover, patient studies conducted thus far have confirmed that one of the especially preferred compounds induces penile erection in impotent males.
Although the compounds of the invention are envisaged primarily for the treatment of erectile dysfunction or sexual dysfunction, they may also be useful for the treatment of female sexual dysfunction including orgasmic dysfunction related to clitoral disturbances.
Generally, in man, oral administration of the compounds of the invention is the preferred route, being the most convenient and avoiding the disadvantages associated with i.c. administration. A preferred dosing regimen for a typical man is 5 to 75 mg of compound three times daily. In circumstances where the recipient suffers from a swallowing disorder or from impairment of drug absorption after oral administration, the drug may be administered parenterally, e.g. sublingually or buccally.
For veterinary use, a compound of formula (I) or a non-toxic salt thereof is administered as a suitably acceptable formulation in accordance with normal veterinary practice and the veterinary surgeon will determine the dosing regimen and route of administration which will be most appropriate for a particular male animal.